Characterization of analgesic and activity effects of methotrimeprazine and morphine.

The interactions of Methotrimeprazine (MTM) with the CNS opiate receptor, with naloxone, and with morphine were investigated. MTM (16--256 nM) did not compete with 3H-naloxone for specific binding sites in mouse brain homogenates. In vivo, MTM induced analgesia was not antagonized by naloxone. After 14 days administration of MTM partial tolerance developed to the activity effect but not the analgesic effect. After 14 days administration of morphine, tolerance developed to both the activity effect and the analgesic effect.